Dengratiols A–D, four new bibenzyl derivatives from Dendrobium gratiossimum

Dengratiol A (1), an unprecedented bibenzyl derivative bearing a tropolone unit together with three pairs of bibenzyl enantiomers (±)-dengratiols B–D [(±)-2–(±)-4], were isolated from Dendrobium gratiossimum Rchb.f. The resolution of enantiomers was performed with chiral HPLC. Their structures were characterized by extensive spectroscopic data analysis and calculated electronic circular dichroism (ECD). A hypothetical biosynthetic pathway for 1...